Estimate torque from a specified per-bolt load, or solve the same approximate torque–preload relation for load, diameter or nut factor. A separate idealized annular seating model preserves the geometry calculation but does not determine a safe joint torque.

Rough torque–preload arithmetic only. Use designer-approved loads and a nut factor matched to the fastener, lubrication and surfaces. This does not establish a safe joint torque or replace the assembly procedure.

Enter the value established for the actual fastener and lubrication. No universal default is supplied.

Gasket Torque Formula

The following is a rough empirical torque–preload approximation. F is the force on one bolt and D is its nominal diameter. Use a nut factor established for the actual fastener, lubrication and surfaces; neither K nor a safe preload is selected by this calculator.

Tg = F × D × k / 1000
  • Where Tg is the Gasket Torque (N-m)
  • F is the bolt load / preload force (N) 
  • D is the diameter (mm) 
  • k is the nut factor (k-value) 

Multiply per-bolt preload by nominal bolt diameter and nut factor, dividing millimeters by 1,000 to obtain meters. The relation is T ≈ K F d. Technetics’ metal-seal catalog describes this as a rough estimate and notes the dependence on joint and friction conditions. It does not verify bolt/flange strength or sealing performance.

How to Calculate Gasket Torque?

The examples below demonstrate arithmetic only; their loads and nut factors are not recommended assembly values. For the separate annular model, area A = π(OD² − ID²)/4, seating-only load W = A × specified seating stress × specified multiplier, and equal per-bolt load is W divided by bolt count. Full-annulus contact and equal loading are assumptions. Pressure end load, effective gasket contact width, relaxation and joint limits require separate design review and a joint-specific assembly procedure. See the scope of ASME PCC-1.

Example Problem #1

  1. First, determine the bolt load / preload force (N). In this example, the bolt load (N) is given as 50,000.
  2. Next, determine the diameter (mm). For this problem, the diameter (mm) is given as 20.
  3. Next, determine the nut factor (k-value). In this case, the nut factor (k-value) is found to be 0.20.
  4. Finally, calculate the Gasket Torque using the formula above: 

Tg =F*D*k / 1000

Inserting the values from above and solving yields: 

Tg =50,000*20*0.20 / 1000 = 200 (N-m)

Example Problem #2

Using the same method as above, determine the variables required by the equation. For this example problem, these are provided as:

bolt load (N) = 60,000

diameter (mm) = 40

nut factor (k-value) = 0.18

Entering these given values yields: 

Tg =60,000*40*0.18 / 1000 = 432 (N-m)